Azure: Reduce manual configuration

[johnbradley]

Right now users must setup fields to specify which backend storage to use:

DukeDSClient/ddsc/config.py

Lines 81 to 84 in 0b4eb27

	AZURE_SUBSCRIPTION_ID = 'azure_subscription_id' # Azure Subscription Id containing the storage account
	AZURE_RESOURCE_GROUP = 'azure_resource_group' # Group within subscription containing the storage account
	AZURE_STORAGE_ACCOUNT = 'azure_storage_account' # Azure Storage Account Name
	AZURE_CONTAINER_NAME = 'azure_container_name' # Container/Bucket/FileSystem name within the Azure Storage Account

This is tedious and error prone.

One option is to search Azure for appropriately setup buckets(containers) and let the user pick if they have multiple.